The objective of the proposed research is to obtain an understanding of the neural oraganization and molecular mechanisms through which arousal states operate to modulate behavior. To this purpose I propose to use the marine mollusk Aplysia californica whose nervous system is highly advantageous for interdisciplinary cellular neurophysiological and neurochemical analyses. In my previous work on Aplysia I identified specific Neurons which mediate the effects of food-induced arousal states on both the feeding system and the cardiovascular system. I now propose to identify higher order neurons which are responsible for maintaining the arousal state. I wish to test a number of hypotheses regarding food-arousal in Aplysia. 1) There exists a single central arousal neuronal system which can affect a variety of behaviors. 2) The arousal state is maintained because the neurons which comprise the system change their properties in such a way that while they are silent in an unaroused state, they become spontaneously active (bursting) in an aroused state. 3) The change to spontaneous activity is due to the firing of cells which release biogenic amines which are capable of activating cyclic nucleotides. 4) The cyclic nueleotides in turn, modify calcium conductances of neurons which are responsible for the bursting characteristics of neurons. To test these hypotheses I intend to use such techniques as intracellular recording and stimulation, voltage clamping and biochemical microtechniques. I hope that by understanding the neural organization and mechanisms involved in the modulation of behavior by arousal states in a simple animal such as Aplysia, a significant insight will be obtained into the nature of these processes in higher animals, thus contributing to our understanding of normal and pathological arousal and activation states in humans.